The 20-year-old man suspected of killing five people with a rifle at a Macy's store had been involved in a string of run-ins with police in recent years, including charges he assaulted his stepfather.
As investigators tried to piece together information on Arcan Cetin, who was arrested on Saturday evening after a nearly 24-hour manhunt, a picture emerged of a troubled young man. Court records show more than a half-dozen criminal cases in Island County alone, stretching back to 2013.
Authorities said the gunman in the attack at the Cascade Mall in Burlington opened fire in Macy's cosmetics department on Friday night, killing a man and four women ranging from a teenager to a senior citizen. The killer then fled.
Cetin said nothing and appeared "zombie-like" when he was taken into custody on a pavement some 30 miles away in Oak Harbor by a sheriff's officer who recognised him as the suspect in the rampage, authorities said. Cetin was arrested near the apartment complex where he was believed to be living.
He had emigrated from Turkey to the US and is a legal permanent resident, officials said.
The FBI said early Saturday there was no indication the shooting was terrorism, but local authorities said later they were ruling nothing out.
On Sunday, investigators searched Cetin's vehicle and the apartment complex and were seen carrying boxes from a rear, upstairs unit. The four-unit building was surrounded with yellow police tape. Detectives would not say what they found.
The Seattle Times reported that court records show he faced three charges of assaulting his stepfather. The newspaper said Cetin was also arrested on drink-driving charges. It gave no details on when the arrests took place or the outcome of the cases.
In the assault case, Cetin was told by a judge last December that he was not to possess a gun, the newspaper reported. However, the stepfather urged the judge not to impose a no-contact order, saying his stepson was "going through a hard time".
Social media accounts apparently belonging to Cetin showed he had a fondness for the military and video games.
Oak Harbor is a city of 22,000 on Whidbey Island with many military families associated with the nearby Naval Air Station Whidbey Island.
Sheriff's Lt Mike Hawley said he spotted Cetin from a patrol car and immediately recognied him as the suspect in the shooting rampage.
"I literally hit my brakes, did a quick turn, I jumped out," Hawley said. "We both jumped out with our guns, and he just froze."
Cetin was unarmed and was carrying a satchel with a computer in it. "He was kind of zombie-like," Hawley said.
No immediate charges were brought against Cetin, who awaited a court appearance on Monday.
The identities of the victims were withheld by police pending post-mortems and notification of family.
But The Seattle Times identified one as 16-year-old Sarai Lara. Her mother said she survived cancer as a young girl and was a happy student.
Authorities in suburban Seattle identified another victim as Belinda Galde, 64, a probation officer with the Snohomish County District Court.